1. Field of the Invention
The present invention relates to a semiconductor light receiving device and a method of manufacturing the same. More particularly, the present invention relates to a semiconductor light receiving device whose light receiving property is improved, and a method of manufacturing the same.
2. Description of the Related Art
A semiconductor light receiving device is known for converting a received light into an electric signal. For example, FIG. 1 is a sectional view showing a configuration of a conventional semiconductor light receiving device.
A conventional semiconductor light receiving device 101 includes: a photodiode unit 102 for converting a received light into an electric signal; and a circuit unit 103 for reading an output of the photodiode unit 102. The manufacturing method is as follows. At first, an n+ type embedding layer 112 is formed in the region of the circuit unit 103 on a p− type substrate 110. After that, so as to cover the entire p− type substrate 110, an n type epitaxial layer 113 is grown. In succession, p+ type embedded layers 104 are diffused at predetermined positions from surface. After that, with the addition of a thermal processing step, the p+ type embedded layers 104 are penetrated to the p-substrate 110. Consequently, the region in the photodiode unit 102 is divided, and the photodiode unit 102 and the circuit unit 103 are insulated and separated. Then, a pn-junction photodiode of the p− type substrate 110 and the n type epitaxial layer 113 is configured. Moreover, a n+ type diffusion layer 105 is formed on the surface of the n type epitaxial layer 113 to obtain a low resistance region. Then, a collector pulling unit 106, a base unit 107 and an emitter unit 108 of the circuit section 103 are sequentially formed to complete the semiconductor light receiving device 101.
In the configuration of the conventional semiconductor light receiving device and the method of manufacturing the same, for the sake of the division of the region in the photodiode unit 102 and the insulation and separation between the photodiode unit 102 and the circuit unit 103, the p+ type embedded layer 104 is diffused at a high concentration from the surface, and the thermal process is then performed at a high temperature. Consequently, the p+ type embedded layer 104 penetrates from the surface to the p− semiconductor substrate 110. Thus, the portion close to the surface of the separating unit (the p+ type embedded layer 104) for the sake of the insulation and separation is formed at the high concentration.
FIG. 2 is a graph showing the concentration profile in the depth direction in the photodiode separating unit (the p+ type embedded layer 104) of the semiconductor light receiving device. The longitudinal axis shows the impurity concentration, and the lateral axis shows the diffusion depth, respectively. With reference to FIG. 2, the highest surface has the highest concentration, and the concentration becomes lower as the depth becomes deeper. Thus, in the conventional semiconductor light receiving device 101, when a blue-violet laser light 109 whose oscillation wavelength (405 nm) is short is emitted to the surface of the photodiode unit 102, the absorption length of light becomes shallow such as 0.1 μm. Thus, the recombination of carries generated in the surface vicinity is great, which results in the drop in the light receiving sensitivity of the photodiode unit 102.
FIG. 3 is a graph showing the light receiving sensitivity in the vicinity of the photodiode separating unit (the p+ type embedded layer 104). The longitudinal axis shows the light receiving sensitivity (arbitrary unit). The lateral axis shows a position where blue-violet laser light is emitted, with the photodiode separating unit (the p+ type embedded layer 104) as the center. As shown in FIG. 1, when the blue-violet laser light 109 is emitted, the range shown by “B′” indicates the light receiving sensitivity of the photodiode separating unit (the p+ type embedded layer 104). That is, it is known that the photodiode separating unit (the p+ type embedded layer 104) has the drop in the light receiving sensitivity indicated as a difference “C′”. This is the drop of about 40%, as compared with the light receiving sensitivity of the photodiode unit 102. A technique is desired for suppressing the drop in the light receiving sensitivity in the photodiode separating unit (the p+ type embedded layer 104), and improving a light receiving performance of the semiconductor light receiving device.
In conjunction with the above description, Japanese Laid Open Patent Application (JP-P 2000-223735A) discloses a semiconductor light receiving device and a method of manufacturing the same. This semiconductor light receiving device includes a plurality of pairs of photodiode units and circuit units. Here, the circuit unit sequentially reads the output of the photodiode unit. This is characterized in that a part of an insulation separation band serving as the insulation separation between the photodiode unit and the circuit unit is formed as LOCOS by LOCOS oxidizing means. The part of the insulation separation band may be formed as the LOCOS by the LOCOS oxidizing means, and the other part may be composed of a P+ embedded layer. The basic structure provided with the substrate and the n+ type embedded layer or epitaxial layer may be contained on the p− type semiconductor substrate. At that time, this has a plurality of pairs of the pn-junction photodiode unit formed from the basic structure and the semiconductor element unit formed such that the collector pulling unit, the base unit and the emitter unit are sequentially added to the basic structure. The part of the insulation separation band for the insulation separation between the pn-junction photodiode unit and the semiconductor element unit is formed as the LOCOS by the LOCOS oxidizing means, and the other part is formed by the P+ embedded layer.
Japanese Laid Open Patent Application (JP-P 2002-100060A) discloses a light receiving element for a recording/reproducing device and a light receiving circuit. The light receiving element in this optical information recording/reproducing device emits a light bean to an optically recording medium and reproduces/erases a record. This is characterized in that a first light receiving unit for receiving a reflection light from the optically recording medium and reading a light beam magnitude at the time of recording and a second light receiving unit for receiving the reflection light from the optically recording medium and reading the information from the optically recording medium are divided and arranged.
Japanese Laid Open Patent Application (JP-P 2002-203954A) discloses a circuit-contained light receiving element. This circuit-contained light receiving element includes: a first-conductive semiconductor lamination structure; a photodiode for converting an input light into an electric signal through a junction with a first second-conductive semiconductor layer formed on the first-conductive semiconductor lamination structure; and a signal processing circuit which is formed in a region different from the photodiode unit in the first second-conductive semiconductor layer and processes an photoelectric converted signal. The first-conductive semiconductor lamination structure has: a first-conductive semiconductor substrate; a first first-conductive semiconductor layer, which is formed on the first-conductive semiconductor substrate and higher in impurity concentration than the first-conductive semiconductor layer; and a second first-conductive semiconductor layer, which is formed on the first-conductive semiconductor layer and lower in impurity concentration than the first first-conductive semiconductor layer. The photodiode is formed in the region surrounded with: a third first-conductive semiconductor layer formed so as to be in substantial contact with the surface of the first first-conductive semiconductor layer; and a fourth first-conductor semiconductor layer formed so as to reach the third first-conductive semiconductor layer from the surface of the first second-conductive semiconductor layer. The signal processing circuit at least includes a transistor of MOS structure.
Japanese Laid Open Patent Application (JP-A-Heisei, 09-283787) discloses a light semiconductor integrated circuit. In this light semiconductor integrated circuit, semiconductor layers of two layers are laminated on the semiconductor substrate, and at least two optical elements are assembled into the semiconductor layer. The portion between the two optical elements is surrounded with a separation region that reaches the semiconductor layer of the second layer from the semiconductor substrate, and the separation region has: a first separation region spreading from the boundary between the semiconductor substrate and the semiconductor layer of the first layer; a second separation region spreading from the boundary between the semiconductor layer of the first layer and the semiconductor layer of the second layer; and a third separation region spreading to the lower layer from the surface of the semiconductor layer of the second layer. In the semiconductor layer of the second layer, the upward diffusion length in the second separation region is set so as to exceed the half of the layer thickness of the semiconductor layer of this second layer. The third separation region overlaps with the tip of the second separation region.